The invention relates to sound motion-picture cameras of the type provided with means for preventing the recording of audio information onto the sound track of the motion-picture film during certain time intervals.
Federal Republic of Germany Offenlegungsschrift 2,333,011 discloses a camera of this general type provided with means for suppressing the recording of sound on the film sound track when the camera is set into operation at the start of the filming of a scene. This serves to prevent the recording of noise and interference signals which are generated during start-up of the electric motor of the drive means for the film transport device, and also to prevent the recording of distorted sound signals during the time interval when the film speed is still building up to its rated value. This is accomplished in that camera by utilizing a field-effect transistor which initially diverts the audio signal from the recording head; thereafter, in order that the suppressing action end after the elapse of a certain time interval, use is made of a capacitor which charges up and after so doing renders the field-effect transistor nonconductive.
This known circuit makes for good sound recording quality, in that the transmission of noise signals and the recording of them onto the film sound track during the start of the filming of a scene are prevented. However, I have found that serious noise and interference signals are generated and that serious frequency distortions develop not only at the start of the filming of a scene, i.e., when the camera is set into operation, but also at the end of the filming of a scene. When the filming of a scene is to be terminated, the activating switch of the camera is released, causing the capstan drive motor to become de-energized and stop and causing the capstan idler roller to be retracted away from the capstan; the circuitry which performs these operations in response to release of the activating switch generates a considerable amount of noise which I find detracts from the quality of the sound recording.